Well if Apple owns IP on it, I guess it would have to be a patent. The hardware would be quite different I guess, so would be a design patent with a max of 15 years from 2001 when the first iPod was released.
I'd guess Apple wouldn't sue, for a design out of patent (so no obligation to defend it) and that they don't even use anymore. (I ANAL)
It would be interesting to use one and see if it feels the same. The original iPods had this very specific feeling to them. If it was replaced with say a glass capacitive circle or it if had different haptic feedback then it would feel quite different.